JDK Code Reading - Data Types

I have a dream to be a code guru someday. It is not only need to write code everyday and also need to read others code. So I start a self long term project to analyze JDK source code. The version of source code used to study is OpenJDK 8u40-b25.

Types in Java

There are two group types in Java

• Primitive
• Object

For each primitive type, Java also provides a boxed (object) types respectively for the reasons

• Treat a data with certain type generically/polymorphically as an Object.
• Use in collection
• Make null value possible

Java supports “auto boxing”. That means, Java can “box” primitive type into its Boxed version or vive versa (“unbox”).

Primitive	Boxed	Description
boolean	Boolean	true or false
byte	Byte	8-bit signed, -2^7~2^7-1
short	Short	16-bit signed, -2^15 to 2^15-1
char	Char	16-bit Unicode
int	Integer	32-bit signed, -2^31~2^31-1
long	Long	64-bit signed, -2^63~2^63-1
float	Float	32-bit floating point
double	Double	64-bit floating point
char[]	String	N-byte Unicode string

We need pay attention, all data of boxed type are immutable.

Boolean